A preferred closure panel operating mechanism disclosed in U.S. Pat. No. 4,403,805 issued Sept. 13, 1983 to Arvin H. Strem et al., raises the closure panel vertically against a downwardly facing roof flange defining the roof opening so that a seal is compressed between the closure panel and the flange to provide a watertight occupant compartment. The closure panel can be tilted or slid for opening or closing by an automatic opening and closing apparatus which is activated by a switch operation of a vehicle driver.
A conventional drive and control unit for a vehicle sun roof or closure panel comprises a resistor which detects the temperature of a motor to sense a loading on the motor. The detected value is compared against an overload reference value so that the motor may be automatically stopped during an overload interval. Such a safety stop measure is relatively simple to achieve in a mechanism having a constant load. However, in a mechanism such as a sun roof mentioned above, when the sun roof is to be opened, it exhibits a high load until the leading end of the panel clears a weather strip, and the magnitude of the load is reduced when the panel clears the strip. Alternatively when the sun roof is to be closed, a link is raised to lift the trailing end of the panel, and as the leading end of the panel moves into contact with the weather strip, the load increases rapidly. In a mechanism including a deflector arm which is located at the front side of a window opening to be erected to drive a deflector when the panel is to be opened and which is collapsed by a panel drive mechanism to turn the deflector down when the panel is closed, a rapid increase in the load occurs when the arm is to be collapsed, and the load experiences a large variation during the normal operation.
Japanese Patent Application No. 131,812/1982, laid open No. 20726/1984, proposes an arrangement which prevents a malfunctioning in the presence of rapid changes in the load. Specifically, the full sliding stroke of a panel is divided into a plurality of sections in a manner to correspond to changes in the load. An overload reference value is previously established for each of the sections. Signal generating means is provided which generates an electrical signal in interlocked relationship with a motor drive mechanism which actually drives a panel, thus deriving a signal which corresponds to a position where the panel has moved as a result of sliding motion. The overload reference value is varied in response to the signal, and is compared against the actual motor load. This arrangement prevents a malfunctioning as a result of variation in the load since overload reference values can be selected in a manner corresponding to the load over the full sliding stroke of the panel.
However, during the full sliding stroke of the panel when the sun roof is to be closed, a portion of the stroke which is immediately preceding to the fully closed position, namely, from the time when the link is raised to lift the trailing end of the panel until the leading end of the panel moves into contact with the weather strip and the panel becomes fully closed by compressing the strip, produces a rapid change in the load. In particular, during the compression of the weather strip, the load increases to a very high value.
Because such stroke portion extends over a reduced distance, a difficulty is experienced in establishing a plurality of overload reference values. Accordingly, a mask interval is established for such stroke portion which deactivates an overload protective device in order to prevent a mistaken judgement that a rapidly increasing load may be misconstrued as a blockage to the full closing by an obstacle.
From the viewpoint of constructing a sun roof mechanism, there exists a small clearance between the leading end of the panel and the front edge of a sun roof opening during the stroke portion extending from a point which immediately precedes the full closure to the fully closed point. In the presence of an obstacle within the clearance, the full closure of the panel is prevented, presenting a high load on the motor. Such clearance may be required in the design of the mechanism, or cannot be removed entirely because of errors associated with the assembly of parts, or may be small enough in the design but may permit an obstacle to be present therein as a result of an assembly operation or a dimensional change occurring subsequent to the assembly.